1. Field of the Invention
The invention relates to a piezoelectric/electrostrictive ceramic composition and a piezoelectric/electrostrictive device using the piezoelectric/electrostrictive ceramic composition.
2. Description of the Background Art
A piezoelectric/electrostrictive actuator has an advantage of being able to precisely control a displacement in sub-micron order. Particularly, a piezoelectric/electrostrictive actuator using a sintered body of a piezoelectric/electrostrictive ceramic composition as a piezoelectric/electrostrictive body can precisely control a displacement and additionally has advantages of high electric-mechanical conversion efficiency, high motive power, high response speed, high durability, and low electric power consumption and using these advantages, the actuator is used for heads of ink jet printers, injectors of diesel engines, and the like.
As a piezoelectric/electrostrictive ceramic composition for piezoelectric/electrostrictive actuators, conventionally Pb(Zr, Ti)O3 (PZT)-type piezoelectric/electrostrictive ceramic compositions have been employed; however the effect of the elution of lead from sintered bodies on the global environments has become a serious concern and since then, a (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition has been investigated.
For example, Yasuyoshi Saito et al, “High Performance Lead-Free Piezoelectric Ceramics in the (K, Na) NbO3—LiTaO3 Solid Solution System”, Ferroelectrics (United States of America), 2006, Volume 338, pp. 17-32 discloses a (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition having a stoichiometric composition.
Further, International Publication No. 2006/095716 discloses that with respect to the (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition, the piezoelectric/electrostrictive property can be improved by making the number of atoms in an A site element in excess of the number of atoms in a B site element.
However, with respect to the conventional (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition, there is a problem that unless the firing temperature is a rather high temperature, sintering cannot be sufficiently promoted and thus the sintered density becomes low and the electric field-induced strain, which is important for a piezoelectric/electrostrictive actuator, cannot be necessarily sufficient at the time of high electric field application.
Further, with respect to the conventional (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition, it is required to carry out firing in an atmosphere enriched in terms of oxygen concentration more than an air atmosphere in order to suppress the evaporation of an alkali component such as Li, and in some cases, it is required to carry out firing in an oxygen atmosphere with an oxygen concentration of 100%. Such a restriction in production leads to an increase in production cost and therefore, it is not desirable.
In addition, the (Li, Na, K)(Nb, Ta)O3 type piezoelectric/electrostrictive ceramic composition has a orthorhombic-tetragonal phase transition temperature (hereinafter, simply referred to as a “phase transition temperature”) TOT and has a characteristic that the electric field-induced strain becomes maximum at a temperature near the phase transition temperature TOT. However, depending on the composition, since the phase transition temperature TOT is out of a practically usable temperature range, it is sometimes impossible to obtain sufficient electric field-induced strain or even if the phase transition temperature TOT is in a practically usable temperature range, since the maximum value of the electric field-induced strain at a temperature near the phase transition temperature TOT cannot become sufficiently high, it is sometimes impossible to obtain sufficient electric field-induced strain at a practically usable temperature.